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This paper presents for the first time the Smart Grid Paradigm: the Link. Having a standardized structure, the Link can be applied to any partition of the power system: electricity production entity, storage entity, the grid or even the customer plant. From this paradigm are extracted three architecture components: the "Grid-Link", the "Producer-Link", and the "Storage-Link". The distributed Link-based architecture is designed. The new architecture allows a flat business structure across the electrical industry and minimizes the amount of the data, which needs to be exchanged. It takes also into account the electricity market rules and the rigorous cyber security and privacy requirements. The interfaces between the all three architecture components are defined. The power system operation processes like load-generation balance, dynamic security and demand response are outlined to demonstrate the architecture applicability. To complete the big picture, the operator role, the corresponding information and communication architecture and the market accommodation are also described.

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This paper introduces a novel local Volt/var control strategy in a low-voltage smart grid. Nowadays, various Volt/var local control strategies built on customer photovoltaic inverters, e.g., cosφ(P) and Q(U), are introduced to mitigate the upper voltage limit violations in feeders with high prosumer share. Nevertheless, although these strategies are further refined by including more local variables, their use is still very limited. In this study, the effects of a new concentrated Volt/var local control strategy in low-voltage grids are investigated. Concentrated var-sinks, e.g., coils-L(U), are set at the end of each violated feeder. The concentrated local control strategy L(U) is compared with the distributed cosφ(P) and Q(U) strategies. Initially, both control strategies are theoretically investigated, followed by simulations in a test feeder. Finally, the expected practical significance of the findings is verified through simulations in a real typical urban and rural grid. Additionally, the impact of the different local control strategies used in low-voltage grids on the behavior of the medium-voltage grid is analyzed. The results show that the concentrated Volt/var control strategy eliminates the violation of upper voltage limit even in longer feeders, where both distributed local strategies fail. In addition, the concentrated L(U) local control causes less reactive power exchange on the distribution transformer level than the distributed cosφ(P) and Q(U) strategies. Therefore, the reactive power exchange with the medium-voltage grid and thus the distribution transformer loading are smaller in the case of concentrated local control strategy.

The major challenge to increase the decentralized generation share in distribution grids is the maintenance of the voltage within the limits. The inductive power injection is widely used as a remedial measure. The main aim of this paper is to study the effect of the reactive power injection (by whatever means) on radial grid structures and their impact on the voltage of the higher voltage-level grids. Various studies have shown that, in addition to the major local effect on the voltage at the injection point, the injection of the reactive power on a feeder has a global effect, which cannot be neglected. The reactive power flow and the voltage on the higher voltage level grid are significantly affected. In addition, a random effect is introduced by the DGs which are connected through inverters (using wind or PVs). Although their operation is in accordance with the grid code, a volatile reactive power flow circulates on the grid. Finally, this study proposes the implementation of the "Volt/var secondary control" interaction chain in order to increase the distributed generation share at every distribution voltage level, be it medium or low voltage, and at the same time to guarantee a stable operation of the power grid. Features of Volt/var secondary control loops ensure a resilient behavior of the whole chain.

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The integration and the effective use of all available energy resourpces are possible only under a global view of the power systems. A holistic approach of the power system control, which includes all voltage levels from high to low voltage and the corresponding commercial model, is represented in the following.